/**
 * Calendar-day helpers, shared by the date filter and the date cell renderer.
 *
 * A calendar day is not an instant. `new Date('2008-09-06')` is UTC midnight,
 * which every local getter then reads back shifted: west of UTC it is the 5th.
 * Everything here works in local date parts so a day stays the day it was
 * written with, whatever zone the browser is in.
 */
/**
 * A `Date` as `YYYY-MM-DD`, read off the LOCAL date parts — `toISOString()`
 * would shift a local midnight to the previous day anywhere east of UTC.
 */
export declare function toIsoDate(d: Date | undefined): string | null;
/** Whether a value is a bare `YYYY-MM-DD` — a calendar day, carrying no instant. */
export declare function isCalendarDay(s: unknown): s is string;
/** A bare day parses as LOCAL midnight; anything with a time/offset as-is. */
export declare function fromIsoDate(s: string | null | undefined): Date | undefined;
/**
 * The calendar day a cell value stands for, as `YYYY-MM-DD`.
 *
 * An ISO string is read as the day it was WRITTEN with — `2026-04-15T17:32+02:00`
 * is the 15th and `1933-04-04T00:00+01:00` the 4th, whatever zone the browser
 * is in. Anything else is parsed and read off its local parts.
 */
export declare function dayOf(cellValue: unknown): string | null;
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